High Nitrate In Happy Brackish Planted Tank

I have a 55 Gallon, sand substrate. Maybe 5 or 6 live plants in it, Java Fern mostly. One driftwood piece.

This tank has super super high Nitrates. I do water changes, and the tank is cycled and established. Running a cannister filter with 3 media and UV.

SG: 1.008 ish
PH: 6.8
Ammonia: 0
Nitrite: 0
Nitrate: 160

I do have a NitraZorb pack, should I stick it in the cannister?

 

Is the driftwood rotting? Do you have any live rock type of rock that could be leeching nitrates into the water? When is the last time you cleaned out the cannister, swished the media around in tank water you were changing? What do you have in the tank (fish) and what percentage of water changes are you doing weekly?

 

Oh...and last but certainly not least...do you have nitrate in your tap water!

 

Is the driftwood rotting? Do you have any live rock type of rock that could be leeching nitrates into the water? When is the last time you cleaned out the cannister, swished the media around in tank water you were changing? What do you have in the tank (fish) and what percentage of water changes are you doing weekly?

Driftwood is not rotting. No nitrates in the water when tested plain. Cannister media was swished 3 months ago roughly. No live rock. Water changes vary but I aI'm for 7 Gallons out of a 55 gallon tank.
Fish are: 4 small mollies, 3 small gobies, 1 medium goby, 2 figure 8 puffers, 1 african chilchid, 1 white tip shark, 1 6 inch common pleco.

I feed them every other day a quarter size amount of various floating and sinking food and twice a week a blood worm tablet or brine shrimp.

 

Have you tested your water with multiple test kits? Nitrate tests can be kinda hard to dial in.

How often do you change your water?

The only thing I can figure is that you're stocked a bit heavily bioload-wise. A common pleco is a pretty large source of waste, and will outgrow that tank pretty quickly. The colombian shark also adds quite a bit, and so do the puffers. If the mollies are breeding as well, those fry are probably dying/getting eaten and adding to the waste.

If it were me, I'd up my water changes to around 15-20 gallons weekly, and maybe work on rehoming that pleco

 

You have some stocking issues, if you want to discuss them, but there are others that can help you with it more specifically, I know for sure a pleco doesn't belong in brackish and neither does an African cichlid. Mollies are fine, puffers are fine ( unless they are the freshwater kind?!) (until/unless they get violent), and depending on the goby they might not be brackish either.
When I had my brackish tank I had a violet goby in it....and a few mollies here and there. My goby was about 13 inches long when he died, I had to do about 25% water changes every week with him, sometimes more, and your bioload is probably very similar to what mine was. I'd up the water changes and rehome the pleco asap! Then go from there.

 

Agreed, you do have a few issues, as not all of those fish are brackish species. If you want some specific help, we're here to help!

You have some stocking issues, if you want to discuss them, but there are others that can help you with it more specifically, I know for sure a pleco doesn't belong in brackish and neither does an African cichlid. Mollies are fine, puffers are fine ( unless they are the freshwater kind?!) (until/unless they get violent), and depending on the goby they might not be brackish either.
When I had my brackish tank I had a violet goby in it....and a few mollies here and there. My goby was about 13 inches long when he died, I had to do about 25% water changes every week with him, sometimes more, and your bioload is probably very similar to what mine was. I'd up the water changes and rehome the pleco asap! Then go from there.

Those puffers are brackish

 

I know the fish are not all brackish, but all of them are brackish tolerable. At 1.006-8 its pretty minimal amount of salt. All of the fish are healthy and growing. The most aggressive one is the Chilchid, he is getting sizable prolly 3 inches now.

I have thought about rehoming the pleco, but he is my oldest fish :/ and we like him a lot.

 

All of them are brackish tolerable, but not for their entire lives. For example: The pleco (disreguarding it's size) will really want soft water to be super healthy. Brackish is going to be pretty hard due to the marine salts. It might not hurt it, but it'll probably weaken it's immune system in the long run and leave it susceptible to infections. The same goes for the cichlid.

Disreguarding the salt factor, the cichlid will probably get a bit too aggressive for the tank anyway. African cichlids, puffers, and mollies really won't mix well IMO, especially once they all hit maturity.

 

All of them are brackish tolerable, but not for their entire lives. For example: The pleco (disreguarding it's size) will really want soft water to be super healthy. Brackish is going to be pretty hard due to the marine salts. It might not hurt it, but it'll probably weaken it's immune system in the long run and leave it susceptible to infections. The same goes for the cichlid.

Disreguarding the salt factor, the cichlid will probably get a bit too aggressive for the tank anyway. African cichlids, puffers, and mollies really won't mix well IMO, especially once they all hit maturity.

When I first added the puffers one was DEFINITELY dominant and actually chewwed the top fin off of the other. Since then they have settled down and they are very docile. Its so funny how curious they are- when I have to go into the tank for anything, they are nipping at my cutucled no afraid of this massive hand at all.

As of right now the Chichlid is only angry during feed time, and then only if there is a hard food object- like a clam or snail.